1. Field of the Invention
The present invention is related to a vehicle anti-theft engine control device, and particularly to a vehicle anti-theft engine control device in which the start-up of an engine is enabled on condition that a predetermined relationship is satisfied by an ID code previously registered in a vehicle ignition or the like and another ID code previously registered on the vehicle side.
2. Description of the Prior Art
In some of the various proposals for preventing the theft of a vehicle such as a ear, the vehicle is prevented from being started or it is immobilized by mechanical and/or electrical means when it is attempted to be started or moved using a wrong key. This is achieved by previously storing an identification code or a key ID code in a key, reading the key ID code when the key is inserted into a key cylinder to start the vehicle, comparing it with a reference ID code prestored in the vehicle side, generating an enable signal only when there is a match between both ID codes, and enabling the engine to be started only when an engine control unit successfully receives tile enable signal. Such a system has been proposed, for instance, in the "Car Technology", Vol. 48, No. 8, 1994, pp. 59-64.
An example of such a conventional transponder type immobilizer is shown in FIG. 6. A key 2 includes a memory (not shown) in which a key ID code (for instance, of 64 bits) is prestored, and a transmitter 4 for transmitting the key ID code. The transmitter 4 of the key 2 and a key cylinder 5 are coupled together by, for instance, an induction coil (antenna) 6.
When the key 2 is inserted into the key cylinder and turned to the ignition ON position, an ignition switch 7 is closed. In response to this, an immobilizer CPU 13 incorporated in an immobilizer HIC 10 in an engine control unit (ECU) 30 operates, and operating electric power is supplied from an antenna unit 19 to the transmitter 4 through the induction coil (antenna) 6. The antenna unit 19 is electrically connected to ECU 30 via a pair of connectors 40 and 50, along with the terminal devices of the drive and control systems essential to the engine control such as the fuel injection valve 17 and the fuel pump 18. The transmitter 4 responds to this to read the key ID code, and transmits it to the key cylinder 5 side.
The received key ID code is amplified by an amplifier (not shown) in the antenna unit 19, read into the CPU 13 through an I/F circuit 12 in the immobilizer HIC 10, and temporarily stored in an appropriate ID code register 13B in the CPU 13. In an EEPROM 14 of the HIC 10, a unique reference ID code assigned to each vehicle is prestored, and the reference ID code and the key ID code which was read in are compared with each other by a compare unit 13S of the CPU 13. If it is determined that there is a match between the two ID codes or they are in a predetermined relationship, an enable code is transmitted from the compare unit 13S to an engine CPU 16. At the same time, a starter relay is activated to initiate the rotation of a starter motor (not shown).
In a ROM 15 of the engine CPU 16, an engine control program is stored which includes at least an engine control algorithm an I/O (Input/Output) control algorithm and an anti-theft algorithm. The engine CPU 16 operates according to the engine control program, and discriminates or verifies the reception of an enable code by the anti-theft algorithm. If the enable code is correct code data, the engine CPU 16 performs a specific control based on the engine control algorithm for the respective terminal devices such as fuel injection valve 17, fuel pump 18 and an ignition control unit 20 connected to the signal port selected by the I/O control algorithm, thereby to enable the start and running of the vehicle.
If the reference ID code stored in the EEPROM 14 and the key ID code transmitted from the key 2 and read in do not match each other or they are not in a predetermined relationship, the compare function unit 13S does not issue an enable code. Accordingly, the start of the vehicle by the CPU 16 is inhibited, and the vehicle's horn is activated by the immobilizer CPU 13 to provide an appropriate alarm.
When the enable code transmitted from the compare unit 13S is not correct code data, the start of the vehicle by the engine CPU 16 is also inhibited. Thus, the illegal start-up of the engine and the driving of the vehicle by a wrong key are prevented to ensure the vehicle anti-theft function.
In the conventional transponder type immobilizer described above, according to the structure wherein the key ID code is compared only once when the power is turned ON, the engine CPU 16 sets "1" (enable) in an engine start enable flag, in which an enabling/disabling of engine control is registered, if the enable code received from an immobilizer HIC 10 is the correct code data; it sets "0" (disable) if the enable code is wrong code data. The enable flag is stored as bit data until the power is turned OFF. After that, the engine CPU 16 periodically checks the enable flag (bit data) and continues the engine control as long as "1" is set (e.g. Japanese Patent Laid-Open No. 54-158532).
if, however, the bit data is changed by a vehicular noise or the like of a traveling vehicle, causing the bit data to be changed to "0" which denotes disable, then the engine CPU 16 undesirably interrupts the engine control.